Calm Mind Cresselia
Cresselia @ Leftovers
Bold Nature
252 HP / 252 Def / 4 Sp.A
-Calm Mind
-Psychic
-Rest
-Sleep Talk
Calm Mind till you get +6 Sp.Attack.Rest and Sleep Talk when necessary.Psychic OHKOs everything not resistant to it after +6 Sp.Attack.Scizor gets 2-3HKOed.(After 6 CMs,Latias's Draco Meteor only does 12% damage.SpecsMence's does only 30%).Bold Nature and 252 Def increases its physical tanking capabilities.You do not need to add EVs into Special Defense because Calm Mind does it for you.
Walling Bronzong
Bronzong @ Leftovers
Bold or Calm Nature
252 HP / 112 Def / 144 Sp.D
-Iron Defense
-Calm Mind
-Stealth Rock / Flash Cannon
-Psychic
Iron Defense up to +6 Defense.Calm Mind up to +6 Special Defense.With +6 Special Attack as well,attack with Psychic and/or Flash Cannon.If you plan as using him as a lead,Stealth Rock can be used over Flash Cannon.
Tanking Mew
Mew @ Leftovers
Docile/Hardy/Quirky/Bashful/Serious Nature
252 HP / 60 Def / 60 Sp.D / 64 Sp.A / 68 Att
-Calm Mind
-Bulk Up
-Flamethrower / Ice Beam / Thunderbolt / Grass Knot / ShadowBall / Baton Pass
-Brick Break / Explosion / Fire Punch / Thunderpunch / Ice Punch / Baton Pass
Calm Mind and Bulk Up to +6 Defense,+6 Attack,+6 Special Attack,+6 Special Defense and sweep.Choose the attacks you want for the most coverage.Baton Pass stat boosts to another sweeper if you are dying.(Deoxys-f is a good receiver).
One slight flaw in your plan: you're never going to get +6 in a competitive metagame unless your opponent is incredibly thick.
Either you'll get Hazed or Roared or beaten down on whichever side of the spectrum you're not improving. Your plan won't work.
Also, neutral natures are useless.
Steel/Psychic gives crap coverage.
Cresselia could work in theory, but other Pokemon do it better.